Many viral methods and non-viral methods have been developed for the purpose of introducing a gene into cultured cells and living tissues for functional analyses of gene and gene therapy (non-patent documents 1 and 2). For introduction of a gene into a cell, a viral method is generally effective. However, the method using a viral vector has a safety problem because of the possibility of parental virus-derived gene introduction and its expression, immunogenicity, and the possibility of modification of host genome structure. On the other hand, many of the non-viral methods using a liposome and the like show lower cytotoxicity and lower immunogenicity than do the viral methods. However, the efficiency of the gene introduction into cultured cells and living tissues tends to be lower than with viral vectors.
“Sendai virus” is a virus belonging to the genus Paramyxovirus in the Paramyxoviridae, possessing cell fusion action. The virion of this virus has on its surface an envelope containing hemagglutinin and neuraminidase, exhibiting polymorphism with a diameter of 150 to 300 nm. Also, Sendai virus has a minus-stranded RNA about 15,500 bases long as the genome, has RNA polymerase, is unstable to heat, agglutinates almost all kinds of erythrocytes, and exhibits hemolytic nature. By inactivating this virus, a Sendai viral envelope vector that has become replication-deficient is obtained.
HVJ attracted attention for fusing Ehrlich tumor cells (non-patent document 3), and analysis of cellular membrane fusion activity (hereinafter fusion activity) has been undertaken and its use as a transgenic vector has been studied. However, HVJ has high immunogenicity and is known to induce CTL particularly when NP protein is produced in a large amount (Cole G. A. et al. Journal of Immunology 158, 4301-4309, 1997). Moreover, inhibition of synthesis of protein by a host is feared. Thus, a method of preparing fused particles (HVJ-liposome) by fusing a liposome including a gene or a protein with HVJ inactivated by ultraviolet irradiation in advance was devised, by which noninvasive gene introduction into a cell or a living organism has been enabled (patent document 1, and non-patent documents 4 and 5).
The present inventors previously developed a novel hybrid transfection vector by combining a virus having a capability of effectively delivering genes (highly efficient) and a non-viral vector with lesser cytotoxicity and immunogenicity (of low toxicity), and constructed a fusion-forming viral liposome having a fusion-forming envelope derived from the hemagglutinating virus of Japan (HVJ; Sendai virus) (Kaneda, 1998; Kaneda et al., 1999). In this delivery system, a DNA-filling liposome is fused with UV-inactivated Sendai virus to form Sendai virus-liposome (400 to 500 nm across), which is a fusion-forming virus-liposome. An advantage of fusion-mediated delivery resides in that the transfected DNA is protected against endosome lysis and lysosome lysis in receptor cells. For example, the DNA incorporated in Sendai virus-liposome can be safely delivered to mammalian cells (Patent document 2). RNAs, oligonucleotides and drugs can also be introduced into cells in vitro and in vivo efficiently. Furthermore, the present inventors invented a transfection vector having an extraneous gene enclosed therein by freeze-drying the Sendai viral envelope or mixing the same with a surfactant, as a transfection vector possessing high transfection activity that is based on a viral envelope, that is safe and stable, and that enables transfection to a broad range of biological tissues (Patent document 3). It is also possible to efficiently introduce a substance into the brain or the central nervous system using the Sendai viral envelope (Patent document 4). Furthermore, the present inventors also found a method wherein a chemotherapy agent such as an anticancer agent is enclosed in the Sendai viral envelope, and transferred into cells or a living organism, and also found that an immune adjuvant effect is obtained (Patent document 4, Patent document 5, Patent document 6).
By the way, a variety of cancer therapeutic methods have already been developed. Treatments for general cancers, particularly solid tumors, include a method wherein an effective drug is transferred to cancer tissue to kill cancer cells. Also, not only chemotherapy or medication therapy involving administration of a chemotherapy agent consisting of a low-molecular compound, but also a variety of therapies such as radiotherapy, immunotherapy, and endocrine therapy have been developed. However, the current situation remains such that it cannot be concluded that solid tumors are completely remittable diseases. Out of solid tumors, prostatic cancers, in particular, develop as cells of the prostate lose their normal cell proliferating function and self-propagate orderlessly. In recent years, the incidence and mortality rates for prostatic cancer patients in Japan have been increasing constantly.
In case of a cancer localized in the prostate, radical prostatectomy is indicated; in recent years, however, patients with early cancers judged to be surgically resectable have been increasing with the spread of screening using the prostate-specific antigen (PSA) marker. However, the frequency of recurrence after surgical resection is reportedly generally 20 to 57%, the still high recurrence rate posing a problem.
Generally, for recurrent cases and prostatic cancers with advances noted outside the prostate, topical radiation irradiation, endocrine therapy and the like are chosen as salvage therapies, but the likelihood of obtaining radical healing is generally low. Hence, neoadjuvant therapy, in which endocrine therapy is performed before surgery, is performed for the purpose of increasing the likelihood of complete resection, but the results obtained are unsatisfactory. Particularly in endocrine therapy, prostatic cancer cells that have acquired hormone refractoriness often emerge, resulting in poorer therapeutic results. For this reason, as the situation stands, there are expectations for the development of a more effective prostatic cancer therapeutic method that will substitute for preoperative endocrine therapy, and a method of efficiently treating hormone-refractory prostatic cancer.